HuR controls apoptosis and activation response without effects on cytokine 3′ UTRs

RNA binding proteins (RBPs) regulate gene expression through several post-transcriptional mechanisms. The broadly expressed HuR/ELAVL1 RBP is important for proper function of multiple cell types in the immune system, and has been proposed to positively control the expression of cytokine and other mRNAs upon activation by regulating their 3′ UTRs. However, this mechanism has not been previously dissected in stable cellular settings. In this study, HuR demonstrated strong anti-apoptotic and activation roles in the Jurkat T cell line. Detailed transcriptomic analysis of HuR knockout cells revealed a substantial negative impact on the activation program, coordinately preventing the expression of several gene categories related to the immune response, including all cytokines. Measurements of IL-2 production showed a significant defect in knockout cells, which was rescued upon reintroduction of HuR. Interestingly, the mechanism of HuR regulation did not involve control of the cytokine 3′ UTRs: HuR knockout did not affect the activity of several cytokine 3′ UTR reporters in 293 cells. Similarly, HuR had no effect on the regulation of IL-2 and TNF 3′ UTRs in resting or activated Jurkat cells. Instead, impaired cytokine production corresponded with defective induction of the IL-2 promoter upon activation. Accordingly, upregulation of the master transcription factor NFATC1 upon activation was also impaired in HuR KOs, without effects on its 3′ UTR. Together, these results indicate that HuR controls cytokine production through coordinated upstream pathways, and that additional mechanisms must be considered in investigating its function. RNA-seq of mRNA in WT and HuR KO Jurkat cells